Conditional entropy and predictability for non-reversible Markov systems

The purpose of this thesis is to clarify the role of non-equilibrium stationary currents of Markov processes in the context of the predictability of future states of the system. Once the connection between the predictability and the conditional entropy is established, we provide a comprehensive approach to the definition of a multi-particle Markov system. In particular, starting from the well-known theory of random walk on network, we derive the non-linear master equation for an interacting multi-particle system under the one-step process hypothesis, highlighting the limits of its tractability and the prop- erties of its stationary solution. Lastly, in order to study the impact of the NESS on the predictability at short times, we analyze the conditional entropy by modulating the intensity of the stationary currents, both for a single-particle and a multi-particle Markov system. The results obtained analytically are numerically tested on a 5-node cycle network and put in correspondence with the stationary entropy production. Furthermore, because of the low dimensionality of the single-particle system, an analysis of its spectral properties as a function of the modulated stationary currents is performed.

GEANT4 Radioprotection studies of the ERHA system for protontherapy treatment

This work is focused on the radiation protection for a protontherapy facility. The aim is to simulate with the best accuracy the prompt radiation field of the proton accelerator situed in Ruvo di Puglia, owned by Linearbeam s.r.l. company. In order to simulate it, is used Geant4, a software for interaction simulations of particles with matter. Thanks to internship work, thesis speaks about cancer therapy with a new method for particle acceleration, a linear beam. For a complete overview of the therapy, this work starts with a crush course on interactions of particle with matter, goes specifically to biological matter, then is shown a brief introduction to shielding studies for a particle acceleration facility, and then a presentation of Geant4. At the end, the main aspects of the proton accelerator are simulated, from proton hitting material of beam-pipe to detectors used to measure dose.

Integrating an Emotion Recognition Model for the Flobi System

This thesis investigates if emotional states of users interacting with a virtual robot can be recognized reliably and if specific interaction strategy can change the users’ emotional state and affect users’ risk decision. For this investigation, the OpenFace [1] emotion recognition model was intended to be integrated into the Flobi [2] system, to allow the agent to be aware of the current emotional state of the user and to react appropriately. There was an open source ROS [3] bridge available online to integrate OpenFace to the Flobi simulation but it was not consistent with some other projects in Flobi distribution. Then due to technical reasons DeepFace was selected. In a human-agent interaction, the system is compared to a system without using emotion recognition. Evaluation could happen at different levels: evaluation of emotion recognition model, evaluation of the interaction strategy, and evaluation of effect of interaction on user decision. The results showed that the happy emotion induction was 58% and fear emotion induction 77% successful. Risk decision results show that: in happy induction after interaction 16.6% of participants switched to a lower risk decision and 75% of them did not change their decision and the remaining switched to a higher risk decision. In fear inducted participants 33.3% decreased risk 66.6 % did not change their decision The emotion recognition accuracy was and had bias to. The sensitivity and specificity is calculated for each emotion class. The emotion recognition model classifies happy emotions as neutral in most of the time.

Spectral properties of resonant Bose-Fermi mixtures

The object of study of the present work are Bose-Fermi mixtures in three dimensions at zero temperature. The system is characterized by a great tunability of physical parameters that is achieved by means of a Fano-Feshbach resonance. As a result, there are mainly two regimes: we move from a situation in which bosons and fermions are weakly interacting to a context in which bosons are coupled to fermions so as to form molecules that are composite fermions, as the coupling between the two types of particles is increased. In the former case, we can describe the mixture as a weakly attractive Bose-Fermi one, while in the latter the same is described in terms of molecules and excess atoms or particles which are unpaired. The main aim of the thesis is to analyze the spectral weight functions which represent the single-particle excitation spectra of the system and are relevant to recent radio-frequency spectroscopy experiments of the system. In order to pursue this objective, diagrammatic methods are used. The formalism is developed within the T-matrix approach: it consists of an approximate calculation whichselects exclusively the class of Feynman’s diagrams that collects all possible repeated boson-fermion interaction.

Quantum Monte Carlo study of effective masses in a polarized unitary Fermi gas

Ultracold gases provide an ideal platform for quantum simulations of many-body systems. Here we are interested in a particular system which has been the focus of most experimental and theoretical works on ultracold fermionic gases: the unitary Fermi gas. In this work we study with Quantum Monte Carlo simulations a two-component gas of fermionic atoms at zero temperature in the unitary regime. Specifically, we are interested in studying how the effective masses for the quasi-particles of the two components of the Fermi liquid evolve as the polarization is progressively reduced from full to lower values. A recent theoretical work, based on alternative diagrammatic methods, has indeed suggested that such effective masses should diverge at a critical polarization. To independently verify such predictions, we perform Variational Monte Carlo (VMC) calculations of the energy based on Jastrow-Slater wavefunctions after adding or subtracting a particle with a given momentum to a full Fermi sphere. In this way, we determine the quasi-particle dispersions, from which we extract the effective masses for different polarizations. The resulting effective masses turn out to be quite close to the non-interacting values, even though some evidence of an increase for the effective mass of the minority component appears close to the predicted value for the critical polarization. Preliminary results obtained for the majority component with the Fixed-node Diffusion Monte Carlo (DMC) method seem to indicate that DMC could lead to an increase of the effective masses in comparison with the VMC results. Finally, we point out further improvements of the trial wave-function and boundary conditions that would be necessary in future simulations to draw definite conclusions on the effective masses of the polarized unitary Fermi gas.